It is a matter of common experience in the oil and gas industry that the drilling of oil or gas wells is carried out with the aid of a circulating drilling mud or drilling fluid. As mentioned in U.S. Pat. No. 3,035,042, issued on May 15, 1962 to Charles H. Hoyt, the circulating drilling fluid serves to cool and lubricate the drill; remove and transport drill cutting to the surface; help the drill bit perform by its hydraulic action; cement or seal the walls of the drill hole; hold the drill cuttings in suspension when drilling is stopped and form a hydrostatic head and thus serve to control the flow of high pressure gas, oil or water.
Also, as discussed in U.S. Pat. No. 3,076,759, issued to Van Dyke et al on Feb. 5, 1963, the most commonly used drilling fluids are aqueous dispersions of clay such as bentonite, illite, kaolinite and other similar materials. As mentioned in this patent, for a drilling fluid to be satisfactorily used in the drilling of wells, it must have sufficiently low viscosity so that it can readily carry rock chips which are loosened by the drill bit to the surface, and it must be thixotropic so taht when the drilling is discontinued, the fluid will gel and prevent the rock chips from settling around the drill bit. Also, it must have the proper yield point to allow resumed fluid circulation when desired.
Another important property of a satisfactory drilling fluid is its ability to seal the porous formations of the well bore. This property is measured by a standard test commonly referred to as water loss, fluid loss or "wall-building".
It has heretofore been difficult, if not impossible, to obtain a drilling fluid having the aforementioned combination of properties without the use of certain additives. Such additives, in the past, included bentonite, starch, gums, tannins, sodium silicate, etc. More recently, however, modified lignosulfonates derived from spent sulfite liquor have proven to be effective additives for attaining the desired properties in a drilling fluid.
Thus, U.S. Pat. No. 2,953,473 issued to King et al on May 3, 1960 discloses a drilling fluid composition which is a combination of drilling mud and specially treated sulfonated lignin-containing material. These sulfonated lignin-containing materials are commonly referred to as "drilling fluid additives" or simply "additives", and their inclusion in the drilling mud or the drilling fluid compositions serves to attain the desired properties which were heretofore discussed.
The sulfonated lignin-containing materials described in the aforementioned King et al patent are derived from spent lignin liquors obtained from the pulping of woods. These sulfonated lignin-containing materials are soluble in the drilling fluid and are highly effective additives in both lime base muds as well as fresh water muds.
In order to improve the effectiveness of the sulfonated lignin-containing materials as drilling fluid additives, King et al recommend converting the sulfonated lignin-containing material to a salt of iron, chromium, copper and aluminum, or combination of said salts. These sulfonated lignin-containing materials comprising said metallic salts are then subjected to oxidation using various oxidants to be hereinafter described. The oxidation changes the constitution of the sulfonated lignin-containing materials and results in additives having enhanced properties.
Alternatively, King et al disclose that the sulfonated lignin-containing materials may be oxidized directly regardless of whether the aforementioned salts are first formed.
With regard to the choice of the oxidizing agents, King et al set forth two criteria; one is the strength and power of the oxidizing agent, and the second is the quantity of the oxidant. The recommended oxidizing agents are those which have a range of oxidation potentials greater than -1.3. These oxidants include hydrogen peroxide, ozone, lead dioxide, chromic acid, chlorine, alkali and alkaline earth hypochlorite, alkali metal chromate (containing chromium ion), alkali metal permanganate (containing manganese ion), alkali metal persulfate, alkali metal perborate, and electrolytic oxidation.
Other patents of interest by way of general background in this field include U.S. Pat. Nos. 2,935,504; 3,007,864; 3,168,511; 3,634,387; 3,686,119 and 4,220,585.
The principal oxidant in Hoyt's U.S. Pat. No. 3,035, 042 is chromium and the additive which is formed is a sulfonated-lignin-iron-chromium complex.
The additive disclosed in the aforementioned patent of Van Dyke et al is also a chromium complex and is substantially iron-free, water-soluble chromium complex of a lignosulfonate.
Although chromium complexed lignosulfonates have achieved a certain degree of acceptability as drilling fluid conditioners, they are environmentally undesirable due to the poisonous nature of chromium. In fact, in several countries including the U.S., legislations have been enacted, are pending, or being considered, prohibiting the use of chromium complexed lignosulfonates due to their adverse impact on the environment.
King et al, in their aforementioned patent, disclose oxidants other than chromium. These patentees also disclose that additives obtained by direct oxidation of lignin-containing materials are less effective than additives obtained by the conversion of the lignin-containing materials to salts, followed by the oxidation of these salts with various oxidants such as those containing the metal ions chromium and manganese which have oxidation potentials greater than -1.3. However, conversion of the lignin-containing materials to their salts, followed by the oxidation of the salts involves a cumbersome and costly procedure.
In my aforementioned application Ser. No. 227,714, I disclose chromium-free, manganese-containing lignosulfonates and chromium-free, ferro-manganese-containing lignosulfonates as drilling fluid additives or conditioners. However, experience has shown that some of these lignosulfonate complexes lack the desired degree of thermal stability at temperatures above 250.degree. F. particularly at low manganese and/or iron levels.
Accordingly, it is an object of the present invention to provide chromium-free drilling fluid additives or conditioners which, in addition to the requisite rheological properties, have higher degree of thermal stability.
It is also an object of this invention to provide such drilling fluid additives or conditioners by complexing manganese lignosulfonates with boron, or boron and iron.
It is a further object of this invention to provide effective and thermally stable drilling fluid additives or conditioners by less cumbersome and more economical procedure than hitherto possible in the prior art methods of making chromium-containing lignosulfonates.
The foregoing and other objects of this invention will be more clearly comprehended from the following detailed description of the invention.